Rtfi Class

Radiographic Interpretation

PART 2

Duties of a Radiographic Interpreter ƒ Mask of any unwanted light from viewer ƒ Ensure the background light is subdued ƒ Check the radiograph for correct identification ƒ Assess the radiographs density ƒ Calculate the radiographs sensitivity ƒ Check the radiograph for any artifacts ƒ Assess the radiograph for any defects present ƒ State the action to be taken, acceptable, rejectable or repair

Radiographic Films

Radiographic Film

Base cellulose triacetate / polyester Base must be :• Transparent - To allow white light to go through • Chemically inert • Must not be susceptible to expansion and contraction • High tensile strength • Flexibility

Radiographic Film Subbing Base Subbing Subbing layer -

the adhesive between the emulsion and base The material for this is gelatine + a base solvent

Radiographic Film Supercoat Subbing

Base Subbing Supercoat

The Emulsion • Consist of millions of silver halide crystal (silver bromide) • The size usually 0.1 & 1.0 µm suspended in gelatin binding medium • Is produced by mixing solution of silver nitrate & salt, such as potassium bromide • The rate & temperature of mixing governs its grain size • Size & distribution of the crystal effect the quality / appearance of final radiograph (large grain more sensitive to radiation)

Pre-exposure

Un-sensitised : Stable

After Exposure

Sensitised : Unstable

During exposure a “latent image” is formed by “sensitised” Silver Halide crystals

LATENT IMAGE

• Silver Bromide crystals are not perfect, they contain “interstitial” silver ions • When an interstitial silver ion accepts a free electron, it becomes a silver atom • The silver atom is larger than the ion and exerts a stress on the crystal lattice • In the presence of developer this stress causes instability and the crystal breaks down

• The interstitial silver atoms nucleate silver crystals • A single interstitial silver atom is sufficient to cause an entire silver bromide crystal to convert to metallic silver • The typical size of a silver bromide crystal in a typical photographic film emulsion is about 1μm • Sensitisation of a silver bromide crystal can be caused by just a single photon of x-ray energy

Radiographic Film What are the advantages of Double Coated Film? • Improve contrast • Reduce the exposure time

Image formation When radiation passes through an object it is differentially absorbed depending upon the materials thickness and any differing densities The portions of radiographic film that receive sufficient amounts of radiation undergo minute changes to produce the latent image (hidden image) 1. The silver halide crystals are partially converted into metallic silver to produce the latent image 2. The affected crystals are the amplified by the developer, the developer completely converts the affected crystals into black metallic silver 3. The radiograph attains its final appearance by fixation

Film Types Grain Size Coarse Medium Fine Ultra Fine

Speed Fast Medium Slow V.Slow

Quality Poor Medium Good V.Good

Film factor 10 35 90 200

Film emulsion produced by mixing solutions of nitrate and salt such as potassium bromide. • The rate and temperature determine the grain structures 1. Rapid mixing at low temperature - Finest grain structure 2. Slow mixing at high temperature - Large grain structure

Film Factor • Is a number relates to the speed of particular film • Is obtained from a films characteristic curve • SCRATA scale often used for film factors :

Smaller film factor - faster the film speed Example • Film factor of 10 will be twice as fast compared to a film factor of 20. • A film factor of 20 took 4min. to expose, 2min will require for a film factor of 10 to gives the same density

100kV Film Type

200kV

Iridium 192

Cobalt

No Screens

Pb Screens

PB Screens

R Factor

KODAK R (single)

20

20

20

FUJI IX25

35

30

KODAK R (double)

35

35

AGFA D2

30

40

FUJI IX29

35

45

FUJI IX50

60

55

50

AGFA D3

55

45

40

FUJI IX59

60

75

FUJI IX80

100

100

100

2.5

100

KODAK M

90

75

60

5.0

45

KODAK B

105

95

100

75

AGFA D4

70

70

65

55

KODAK T

140

115

100

75

AGFA D5

120

115

105

95

FUJI IX100

200

190

210

1.0

210

KODAK AA

200

200

150

1.1

150

AGFA D7

220

180

170

FUJI IX150

370

340

400

KODAK CX

300

250

200

255

AGFA D8

315

260

265

260

35

Pb Screens

R Factor

25

5.0

50

14.0

30

5.0

2.0

155 0.6

410

0.9

Characteristics Extremely fine-grained film with low speed and high contrast. Ideal for exposures where the finest possible detail is required.

D2 D3 S. C.

Single-emulsion film with very high image quality, maximum perceptibility, high contrast and pleasant image tint. The ideal film for sharp enlargements. The colorless back coating prevents curling to guarantee a film that remains flat under all conditions.

D3

An ultra fine-grained film with low speed and high contrast that obtains a high detail perceptibility. D3 meets the requirements of the nuclear industry.

D4

The ideal standard film for high quality applications. An extra fine grain film with average speed and high contrast.

D5

The fastest film for fine detailed applications. A fine grain, moderate speed film with high contrast. High image quality, excellent consistency and homogeneity, pleasant image tint and a shiny surface.

D7

The ideal standard film for those applications where the emphasis is on short exposure time. A fine grained film with excellent image quality and high contrast. D7 is a high speed film used for high energy applications, with particularly good consistency, homogeneity, a pleasant image tint and shiny surface.

D8

Ultra-high speed fine grain film, with moderate contrast designed for exposures with or without metal screens. If a higher speed is required. D8 also can be used with fluorometallic (RCF) or fluorescent screens (bivalent type).

D6R

D6R, an extra-fine grain film, can be processed both in a standard 8 min. cycle and in a short 2 min./90 sec. cycle. Designed for exposures with or without metal screens, flourometalic (RCF), and fluorescent screens (bivalent type).

Film

Features

lx 25

Fuji's finest grain, high contrast ASTM Class 1 film having maximum sharpness and discrimination characteristics. It is suitable for new materials, such as carbon fiber reinforced plastics, ceramic products, and micro electric parts. lx25 is generally used in direct exposure techniques or with lead screens. lx25 is recommended for automated processing only.

lx 50

An ultra-fine grain, high contrast ASTM E94 Class 1 film having excellent sharpness and high discrimination characteristics. It is suitable for use with any low atomic number material where fine image detail is imperative. Its ultra-fine grain makes it useful in high energy, low subject contrast applications where high curie isotopes or high output X-ray machines permit its use. Wide exposure latitude has been demonstrated in high subject contrast applications. IX 50 is generally used in direct exposure techniques or with lead screens.

lx 80

An extremely fine grain, high contrast ASTM Class 1 film suitable for detection of minute defects. It is applicable to the inspection of low atomic number material with low kilovoltage X-ray sources as well as inspection of higher atomic number materials with high kilovoltage X-ray or gamma ray sources. Wide exposure latitude has been demonstrated in high subject contrast applications. IX 80 is generally used in direct exposure techniques or with lead screens.

lx 100

A very fine grain, high contrast ASTM Class 2 film suitable for the inspection of light metals with low activity radiation sources and for inspection of thick, higher density specimens with high kilovoltage X-ray or gamma ray sources. Wide exposure latitude has been demonstrated in high contrast subject applications. Although IX 100 is generally used in direct exposure techniques or with lead screens, it is suitable for use with fluorescent or fluorometallic screens.

lx 150

A high speed, fine grain, high contrast ASTM Class 2 film suitable for inspection of a large variety of specimens with low-to-high kilovoltage X-ray and gamma ray sources. It is particularly useful when gamma ray sources of high activity are unavailable or when very thick specimens are to be inspected. It is also useful in X-ray diffraction work. IX 150 is used in direct exposure techniques or with lead screens.

Processing Film

Fixer

bath

Stop

Developer

Processing Systems

Manual System

Running water

Processing Systems Development •Metallic Silver converted into Black metallic silver 3-5 min at 20OC •The developer supplies a source of electrons (-ve ions) which cause the chemical changes in the emulsion. Main Constituents Developing agent metol-hydroquinone Accelerator keeps solution alkaline Restrainer ensures only exposed silver halides converted Preservative prevents oxidation by air Replenishment Purpose – to ensure that the activity of the developer and the developing time required remains constant Guideline – 1. After 1m2 of film has been developed, about 400 ml of replenisher needs to be added

Developer Constituents

Action

Chemicals in common use

Developing agent(s)

Preferentially reduces the exposed silver halide crystals (+ve ions) to black metallic silver.

Metol. Hydroquinone. Phenidone

Accelerator

A chemical which gives an alkaline reaction which speeds up development.

Borax. Sodium carbonate. Sodium hydroxide.

Preservative

Prevents oxidation of the developer.

Sodium sulphate.

Restrainer

Controls the level of development fogging.

Potassium bromide.

Sequestering agent

Prevents the formation of scale.

Sodium. Hesametaphosphate.

• The film are agitated for approximately 20 seconds and then for approximately 10 seconds every minute. • Agitation allows for fresh developer to flow over the film and prevents the possibility of bromide streaking;

Processing Systems

Stop Bath 3% Acetic acid - neutralises the developer

Processing Systems Fixer • Sodium thiosulphate or ammonium thiosulphate Functions:- 1. Removes all unexposed silver grains 2. Hardens the emulsion gelatin 3. Convert the unwanted unexposed halides into water soluble compounds; then readily dissolved or removed at the final wash stage. • Clearing time - The time taken for the radiography to loose its milky appearance. Fixing time - Twice the clearing time

Processing Systems

Washing • Films should be washed in a tank with constant running water for at least 20 minutes. • Insufficient washing the film can caused the yellow fog appears. • Usually followed by dipping in a clean water bath containing a wetting agent which helps to promote even drying. • Overwashing will cause swelling and excessive softening of the film emulsion, a major cause of “drying marks”.

SENSITOMETRY

Characteristic Curves • Increasing exposures applied to successive areas of a film • After development the densities are measured • The density is then plotted against the log of the exposure Characteristic curve Sensitometric curve Hunter & Driffield curve

Characteristic Curves 4.0

3.5

Density

Shoulder

3.0

2.5

Average gradient - Straight line

2.0

1.5

1.0

Toe portion 0.5

Base fog 0.3

0

0.5

1.0

1.5

2.0

2.5

3.0

Characteristic Curves The relationship between exposure time and resultant film density is non-linear The gradient of the film characteristic curve is a measure of film contrast

Characteristic Curves Information which can be obtained from a films characteristic curve • The position of the curve axis gives information about the films speed • The gradient of the curve gives information on the films contrast • The position of the straight line portion of the curve against the density axis will show the density range within which the film contrast will be at its highest. • New exposure time can be determined for a change of film type

Characteristic Curves

Density (Log)

Density obtained in a photographic emulsion does not vary linearly with applied exposure

The steeper the slope the greater the contrast

Log Relative Exposure

Characteristic Curves Information which can be obtained from a films characteristic curve •The position of the curve axis gives information about the films speed A

B

C

D

E

Film A is faster than Film B

Density

Film B faster then C

Log Relative Exposure

• Film A is coarse grain & is faster than Film B & C • Film B is fine grain and it’s speed is intermediate between Film A & C • Film C is ultra-fine grain and is the slowest of the three • A “fast” film requires a shorter exposure time than a “slow” film

Characteristic Curves Information which can be obtained from a films characteristic curve • The position of the curve axis gives information about the films speed • The gradient of the curve gives information on the films contrast • The position of the straight line portion of the curve against the density axis will show the density range within which the film contrast will be at its highest. • New exposure time can be determined for a change of film type

Changing Density Density achieved

1.5

Density required

2.5

Density 2.5

Determine interval between logs 1.8 - 1.3 = 0.5 1.5

Antilog of 0.5 = 3.16 Therefore multiply exposure by 3.16

1.3 1.8

(measured density is lower than the required density)

Original exposure 10 mA mins New exposure 31.6mA mins

Log Relative Exposure

1.63 - 1.31 = 0.32 Antilog 0.32 = 2.1 Original Exposure = 10 mAmin

Using D7 Film a New Exposure = 2.1 X 10 = 21 mAmin density of 1.5 was achieved using an exposure of 10 mAmin What exposure is required to achieve a density of 2.5?

Characteristic Curves Information which can be obtained from a films characteristic curve • The position of the curve axis gives information about the films speed • The gradient of the curve gives information on the films contrast • The position of the straight line portion of the curve against the density axis will show the density range within which the film contrast will be at its highest. • New exposure time can be determined for a change of film type

Changing Film Obtain Logs for Films A and B at required density

Density

A

B

2.5 Interval between logs 1.85 – 1.7= 0.1 Antilog of 0.15 = 1.42

Multiply exposure by 1.42 Original exposure = 10 mA mins New exposure

= 10mAmins. X 1.42 = 14.2 mA mins

1.7 1.85 Log Relative Exposure

2.07 - 1.63 = 0.44 Antilog 0.44 = 2.75 Original Exposure = 10 mAmin New Exposure = 2.75 X 10 = 27.5 mAmin

Using D7 Film a density of 2.5 was achieved using an exposure of 10 mAmin What exposure is required to achieve a density of 2.5 using MX film?

Characteristic Curves BASE FOG LEVEL (AFFECTS FILM CONTRAST) National standards generally limit the base fog level of unexposed radiographic film to 0.3. If the base fog level exceeds this value film contrast can be quite severely affected. Fog level can be checked by processing a sample of the unexposed film.

Characteristic Curves

BASE FOG LEVEL (AFFECTS FILM CONTRAST) Effect of film fogging on the film characteristic curve

(The dotted lines show the average gradient between a film density of 1.5 and a film density of 2.5 for film having a base fog level of 0.1 and 0.5 respectively. The average gradient with a base fog level of 0.1 is about 3.6 while that for a base fog level of 0.5 is about 2.7. This decrease in average gradient is indicative of a reduction in film contrast.)

RADIOGRAPHIC DEFINITION DEFINITION • Is the sharpness of the dividing line between areas of different density • Usually is not measured exclusively, normally assessed subjectively • Measured by the use of Duplex type III IQI (Bs EN 462:P5)

Radiographic Definition

Alternative terms given •Duplex type •Cerl type B

EN 462-5

Definition measured by the use of a type III I.Q.I.

•EN 462 part 5 Consists of pairs of parallel platinum or tungsten wires of decreasing thicknesess The gap same as the thickness wire

Radiographic Definition Geometry Unsharpness ( Ug) • Also known as Penumbra is the unsharpness on the radiograph caused by the geometry of the radiation in relation to the object/subject • Always exists & borders all density fields

Inherent unsharpness (Ui) • Unsharpness of the radiographs caused by stray electrons transmitted from exposed crystal which have affected adjacent crystal • Always exists; depending on grain size, distribution & energy used • Increases with a reduction in wavelenght

Inherent Unsharpness Stray electrons from exposed crystals

-

-

-

Exposed radiograph with crack like indication

-

-

-

-

-

Adjacent crystals affected by stray electrons

Calculation of geometric unsharpness (Ug 2mm dia.

Focal / Source SIZE

2mm length FOD / SOD

FFD / SFD

S = 2² + 2² = 2.82mm Typical maximum penumbra of 0.25 mm is often used.

OFD

Film

ug

ug

Two circular objects can be rendered as two separate circles A or as two overlapping circles B depending on the direction of the radiation

Long OFD

Short OFD

Lack of parallelism

Short FFD

Long FFD

DEFINITION Radiographic Definition

Geometric unsharpness

Inherent unsharpness

• FFD/SFD too short

• Coarse grain film

• OFD too large/screen film contact

• Salt screens

• Source size too large

• Radiation quality

• Vibration/movement

• Development

• Abrupt thick. Changes in specimen

Geometry of Image Formation

Penumbra Ug) Focal spot size, F

Ug= F x ofd fod

fod ffd

(Ug = 0.25mm)

ofd

Penumbra (Ug) To minimise penumbra „

Source size as small as possible

„

Source to object distance as long as possible

„

Object to film distance as small as possible

Penumbra Calculations Penumbra = S = 4mm OFD = 25mm FFD = 275mm

S x OFD FFD - OFD

Penumbra Calculations Min FFD =

S x OFD Penumbra

S = 4mm OFD = 25mm FFD = 275 Penumbra = 0.25

+ OFD

Inherent Unsharpness „

Large film grain size increased inherent Unsharpness

„

Short wavelength increased inherent Unsharpness

„

Loose film crystal distribution increased inherent Unsharpness

Geometric Unsharpness

Geometric Unsharpness Long Film to Focal Distance

Geometric Unsharpness Short Focal to Object Distance

Geometric Unsharpness Small Focus

Geometric Unsharpness Large Focus

Geometric Unsharpness Short Object to Film Distance

Geometric Unsharpness Long Object to Film Distance

Intensifying Screens Radiographic film is usually sandwiched between two intensifying screens There are three main types of intensifying screens • Lead screens • Fluorescent screens • Fluorometallic screens

Lead Intensifying Screens „

Film placed between 2 intensifying screens

„

Intensification action achieved by emitting particulate/beta radiation (electrons)

„

Generally lead of 0.02mm to 0.15mm

„

Front screen shortens exposure time and improves quality by filtering out scatter

„

Back screen acts as a filter only

Salt Intensifying Screens ƒ

Intensification action achieved by emitting Light radiation (Visible or UV-A)

ƒ ƒ ƒ ƒ ƒ

Intensification action twice that of lead screens No filtration action achieved Salt used calcium tungstate Film placed between 2 intensifying screens 2 types – 1. high definition (fine grain screen) 2. high speed or rapid screen

Fluorometallic Intensifying Screens ƒ ƒ ƒ ƒ ƒ ƒ

Film placed between 2 intensifying screens Intensification action achieved by emitting light radiation (Visible or UV-A) and particulate radiation electrons) High cost Front screen acts as a filter and intensifier Salt used calcium tungstate Screen type 1. Type 1 – x-rays up to 300kV 2. Type 2 – x-rays 300-1000kV, Ir 192 3. Type 3 – Co60

Film Latitude Latitude – Range of thickness Wide latitude radiographic films meet the applications for a variety of multi-thickness subjects. (fuji IX 29 & 59)

Wide latitude

Low latitude

Poor contrast Good definition

Good contrast Poor definition

Scatter • Radiation emitted from any other source than that giving the primary desired rectilinear propagation (straight line) • Scatter will lead to - poorer contrast - poorer definition and - create spurious indications

• It may also cause radiological protection problems

Scatter • Internal scatter originating within the specimen • Side scatter walls and nearby objects in the path of the primary beam • Back scatter materials located behind the film

Scatter • Internal scatter

originating within the specimen

Scatter • Side scatter

walls and nearby objects in the path of the primary beam

Scatter • Back scatter

materials located behind the film

Back Scatter Notification The presence of back scattered radiation must be checked for each new test arrangement by a lead letter B placed immediately behind each cassette. If the image of this symbol records as a lighter image on the radiograph, it shall be rejected. If the symbol is darker or invisible the radiograph is acceptable and demonstrates good protection against scattered radiation.

SCATTER

Control of Scatter • • • • • • •

Collimation Diaphragms Beam filtration Masking or Blocking Grids Filters Increased beam energy

COLLIMATION • provide radiation safety to the operating personnel and general public by directing the emerging radiation beam to the useful area of exposure. • X-ray equipment is always to some extent selfcollimated • which is turn results in radiographs with better sensitivity. • In gamma radiography collimators consisting of hollowed out blocks of lead weighing around 2.5 kg are common. • collimators for gamma radiography are made from tungsten or tantalum. • The principle of collimation is if there is less radiation then there will be proportionally less scatter.

Diaphragms • They consist of a sheet of lead which has a hole cut in it the same shape as the object which is being radiographed. • shield out all unwanted radiation, the set up for radiography must however, be extremely accurate if the use of a diaphragm is to be successful. • Diaphragms are therefore more likely to be seen where a fully automated technique is in use that allows for a very high degree of repeatability in the set up accuracy.

Shutters and masks • consists of placing sheets of lead, bags of lead shot or barium putty or any other radiation absorbing material around the object which is being radiographed in order to reduce the undercutting effect of side scatter. • limit the radiation beam as it is directed toward the part, thereby decreasing scatter radiation by narrowing and decreasing beams to a specific location. • Shutters are usually mounted on the front of the image intensifier and help keep radiation not passing through the part from impinging on image intensifier screen and causing phosphor blooming.

GRIDS • limited to medical radiography. • A grid consists of a matrix of parallel metal bars which is set in oscillation during exposure such that the grid itself does not produce a radiographic image. • effective method of reducing the effects of side scatter, but grids are very rarely a practical option for industrial situations. • In order to be effective the grid must be placed as close as possible to the film. • In microfocus x-radiography it may be placed between the film and the object.

Sensitivity Sensitivity • Defined as the smallest indication or detail can be seen on the radiographs. • It is a function of the contrast and the definition of the radiographic image. • A general term of sensitivity can be determine as an overall assessment of the quality on a radiographic image which relates to the ability radiographic techniques to detect fine discontinuities. . • Image quality is determined by a combination of variables: radiographic contrast and definition.

Sensitivity

IQI sensitivity

Defect sensitivity

The image on a radiograph which is used to determine the quality level

Ability to assist the sensitivity and locate a defect on a radiograph

(Depend on the defect orientation)

IQI Sensitivity „ „

Ideally IQI should be placed on the source side IQI sensitivity is calculated from the following formula

Sensitivity % = Thickness of thinnest step/wire visible x 100 Object Thickness

Image Quality Indicators Thickness (mm) 0.050 0.063 0.08 0.10 0.125 0.15 0.16 0.20 0.25 0.30 0.32 0.35 0.40 0.50 0.60 0.63 0.75 0.80 0.90 1.00 1.20 1.25 1.50 1.60 1.80 2.00 2.50 3.00 3.20 4.00 5.00 6.30

BS 3971 1-6

STEP 7-12

13-18

4-10

6

7 6 5 4

5 4 3

3 2 1

WIRE 9-15

15-21

DIN 54 109 WIRE (DIN 62) 1-7 6-12 10-16

H1

BS EN 462-2 STEP/HOLE H5 H9

H 13

W1

BS EN 462-1 WIRE W6 W 10

7 6

6

7 6

5 4 3

7

5 4 3

7 6

7

5 4 3

2

5

6

2

2

6

6

2

1

5 4

1

1

5 4

5 4

1

6

4 3

5

2

3

3

3

4

1

7

7

2

2

6

7

2

3

6

6

1

1

5

6

1

2 1

5 4

5

4

5

4

3

4

3 2

2 1

6 5 4 3 2 1

3 2 1

1

6 5

3 2

4 3 2 1

1

W 13 7 6 5 4 3 2 1

IQI Sensitivity A Radiograph of a 16mm thick but weld is viewed under the correct conditions, 5 wires visible on the radiograph IQI pack 6-12 Din 62, what is the IQI sensitivity? Sensitivity = Thickness of thinnest wire visible X 100 Total weld thickness

IQI Sensitivity Using the same IQI pack 6-12 Din 62, How many IQI wires must be visible to give an IQI sensitivity of 2 %, thickness of material 16mm

Image Quality Indicator

Image Quality Indicators ƒ

IQI’s / Penetrameters are used to measure radiographic sensitivity and the quality of the radiographic technique used.

ƒ

They are not used to measure the size of defects detected

ƒ

Standards for IQI’s include:

BS EN 462-1 – Wire Type BS EN 462-2 – Step/wedge Type BS EN 462-3 – Classes for ferrous mat. BS EN 462-4 – IQI values & tables BS EN 462-5 – Duplex WireType

BS 3971 DIN 54 109 ASTM E747

BS EN 462-1 wire type IQIs each consist of 7 wires taken from a list of 19 wires. Four standard wire groupings are available, designation designation designation designation

‘W1’, wires 1 to 7, ‘W6’, wires 6 to 12, ‘W10’, wires 10 to 16 ‘W13’, wires 13 to 19.

Each of these groupings is available in any of 4 types of material; ‘FE’, ‘CU’, ‘AL’ ‘TI’.

for Steel or stainless steel for copper, tin, zinc and their alloy for Aluminium for Titanium

EN 462-1 wire type IQIs

Designation

Diameter

W1

3.2

W2

2.5

W3

2.0

W4

1.6

W5

1.25

W6

1.0

W7

0.8

W8

0.63

W9

0.5

W10

0.4

W11

0.32

W12

0.25

W13

0.2

W14

0.16

W15

0.125

W16

0.1

W17

0.08

W18

0.063

W19

0.05

BS EN 462-1 wire diameters

Easy to remember the wire diameters: Remember the diameters of the first three, 3.2, 2.5 and 2.0 mm divide by halve from the remaining value.

ASTM E 747 The series consists of 21 wires ranging from 0.08 mm to 8.1 mm in diameter; there are 4 overlapping groups of 6 wires, each designated by a letter (A, B, C or D) IQI type

WIRE DIAMETERS

A

0.08

0.1

0.13

0.16

0.2

0.25

B

0.25

0.33

0.4

0.5

0.63

0.81

C

0.81

1.0

1.27

1.6

2.0

2.5

D

2.5

3.2

4.0

5.1

6.3

8.1

BS EN 462-2 Step-hole IQIs

Classification of radiographic techniques The radiographic techniques are divided into two classes: — class A: basic techniques; — class B: improved techniques. Class B techniques will be used when class A might be insufficiently sensitive. Better techniques compared to class B are possible and may be defined by specification of all appropriate test parameters. The choice of radiographic technique shall be defined by specification. If, for technical reasons, it is not possible to meet one of the conditions specified for class B, such as type of radiation source or the source-to-object distance, f, it may be defined by specification that the condition selected may be that specified for class A. The loss of sensitivity shall be compensated by an increase of minimum density to 3,0 or by the choice of a higher contrast film system. Because of the better sensitivity compared to class A, the test specimen may be regarded as tested within class B. This does not apply if the special SFD reductions as described in 6.6 for test arrangements 6.1.4 and 6.1.5 are used.

CLASS ‘A’ RADIOGRAPHY

CLASS ‘B’ RADIOGRAPHY

1. Single Wall Technique Source Side IQI Thickness

Required wire

1. Single Wall Technique Source Side IQI

Wire diameter

Average Sensitivity

≤ 1.2

18

0.063

> 5.25%

> 1.2 ≤ 2

17

0.08

5%

> 2 ≤ 3.5

16

0.1

3.64%

> 3.5 ≤ 5

15

0.125

2.94%

>5≤7

14

0.16

2.67%

> 7 ≤ 12

13

0.2

2.1%

> 12 ≤ 18

12

0.25

1.67%

> 18 ≤ 30

11

0.32

1.33%

> 30 ≤ 40

10

0.4

1.14%

> 40 ≤ 50

9

0.5

1.11%

> 50 ≤ 60

8

0.63

1.14%

> 65 ≤ 85

7

0.8

1.07%

> 85 ≤ 120

6

1.0

0.98%

> 120 ≤ 220

5

1.25

0.74%

> 220 ≤ 380

4

1.6

0.53%

> 380

3

2.0

< 0.53%

Thickness

Required wire

Wire diameter

Average Sensitivity

≤ 1.5

19

0.05

> 3.33%

> 1.5 ≤ 2.5

18

0.063

3.15%

> 2.5 ≤ 4

17

0.08

2.46%

>4≤6

16

0.1

2.0%

>6≤8

15

0.125

1.79%

> 8 ≤ 12

14

0.16

1.6%

> 12 ≤ 20

13

0.2

1.25%

> 20 ≤ 30

12

0.25

1.0%

> 30 ≤ 35

11

0.32

0.98%

> 35 ≤ 45

10

0.4

1.0%

> 45 ≤ 65

9

0.5

0.91%

> 65 ≤ 120

8

0.63

0.68%

> 120 ≤ 200

7

0.8

0.5%

> 200 ≤ 350

6

1.0

0.36%

> 350

5

1.25

< 0.36%

EN 462-5

Image Quality Indicators

7FE12

Step / Hole type IQI

Wire type IQI

Image Quality Indicators

IQI wire thickness

=

Subject thicknes 100

x 2

ASME Image Quality Indicators 4T dia T dia 2T dia

Penetrmeter Design 0.5mm

17

Minimum Penetrmeter Thickness (2% of the weld thickness) Minimum Diameter for 1T Hole Minimum Diameter for 2T Hole Minimum Diameter for 4T Hole

0.5mm 1.0mm 2.00mm

12mm 38mm

IQI Sensitivity 1 Hole visible = 4T 2 Holes visible = T 3 Holes visible = 2T

T

Image Quality Indicators It is important that IQIs are placed

Step/Hole Type IQI

Wire Type IQI

Placement of IQI • IQI must be placed on the maximum thickness of weld • Thinnest required step or wire must be placed at the extreme edge of section under test • IQI must be placed at the source or film side and at a position within the diagnostic film length (DFL) in accordance with the requirements of the contract specification. • In case of access problem , IQI has to placed on the film side of the object, letter ‘FS’ should be placed beside the IQI. • IQI material chosen should have similar radiation absorption/transmission properties to the test specimen

Radiographic Techniques

Radiographic Techniques „

Single Wall Single Image (SWSI) - film inside, source outside

„

Single Wall Single Image (SWSI) panoramic - film outside, source inside (internal exposure)

„

Double Wall Single Image (DWSI) - film outside, source outside (external exposure)

„

Double Wall Double Image (DWDI) - film outside, source outside (elliptical exposure)

„

Double Wall Double Image (DWDI) - film outside, source outside (superimposed)

„

Parallax / Tube shift method - to determine the distance/depth of the defect

Single wall single image SWSI

Film Film

IQI’s should be placed source side

Single wall single image SWSI panoramic

Film • IQI’s are placed on the film side • Source inside film outside (single exposure)

Double wall single image DWSI

Film • IQI’s are placed on the film side • Source outside film outside (multiple exposure) • This technique is intended for pipe diameters over 100mm

Double wall single image DWSI Identification • Unique identification

EN W10

• IQI placing • Pitch marks indicating readable film length

A

B ID MR11 Radiograph

Double wall double image DWDI elliptical exposure

• • • •

Film IQI’s are placed on the source side Source outside film outside (multiple exposure) A minimum of two exposures This technique is intended for pipe diameters less than 100mm

Double wall double image DWDI Identification

4

EN W10

3

• Unique identification • IQI placing • Pitch marks indicating readable film length

1

2 ID MR12

Shot A Radiograph

Double wall double image (DWDI) perpendicular exposure

Film • • • • •

IQI’s are placed on the source side Source outside film outside (multiple exposure) A minimum of three exposures Source side weld is superimposed on film side weld This technique is intended for small pipe diameters

Sandwich Technique It may be used on components where there are substantial thickness differences

Density 3.0

Density 1.2

Density 3.0

Density requirement 2.0 to 3.0 Density unacceptable

Density 1.2

Sandwich Technique

LEAD SCREENS

FILM A FILM B

Density 3.0

Density 2.0

FILM A: Fast film - Thicker section FILM B: Slow film - Thinner section

FILM A FILM B

Density 3.0

Density 2.0

Density 2.0 to 3.0 acceptable

Parallax technique

• The parallax radiographic technique may be used to determine the depth of defects below the surface • This may be useful to know for repair purposes. • It is a technique more applicable to thick specimens, eg. over 50mm, but is rarely used • Also known as a Tube Shift Method

Parallax technique

Alignment of beam The beam of radiation shall be directed to the centre of the area being inspected and should be normal to the object surface An appropriate alignment of the beam can be permitted if it can be demonstrated that certain inspections are best revealed by a different alignment of the beam Between the contracting parties other ways of radiographing may be agreed upon.

Interpretation conditions

Duties of a Radiographic Interpreter ƒ Mask of any unwanted light from viewer ƒ Ensure the background light is subdued ƒ Check the radiograph for correct identification ƒ Assess the radiographs density ƒ Calculate the radiographs sensitivity ƒ Check the radiograph for any artifacts ƒ Assess the radiograph for any defects present ƒ State the action to be taken, acceptable, rejectable or repair

Viewing conditions • Darkened room • Clean viewer • Minimum adequate illumination from the viewer is 3000cd/m2 • Eyesight must be adjusted to the darkened conditions • Comfortable viewing position and environment • Avoid fatigue

Radiographic Quality „

Density - relates to the degree of darkness

„

Contrast - relates to the degree of difference in density between adjacent areas on a radiograph

„

Definition - relates to the degree of sharpness

„

Sensitivity - relates to the overall quality of the radiograph

Factors Influencing Sensitivity

Sensitivity

Contrast

Definition

Radiographic Quality • Density • Contrast

The ability to differentiate areas of different film density

Contrast Radiographic contrast :- The density difference on a radiography between two areas- usually subject and the background (overall) Subject contrast

:- Contrast arising from variation in opacity within an irradiated area

Film contrast

:- The slope of characteristic curve of the film at specified density. ( Type of film being used, fine grain or large grain)

Radiographic Contrast Subject contrast is governed by the range of radiation intensities transmitted by the specimen. A flat sheet of homogeneous material of nearly uniform thickness would have very low subject contrast. Insufficient Contrast • kV too high • Over exposure compensated for by shortened development • Incorrect film - screen combination

Excessive Contrast • kV too low • Incorrect developer

Factors Influencing Sensitivity Sensitivity Definition

Contrast

Density

Time

Film

Energy

Temperature

Object contrast

Type

Strength

Processing

Agitation

Radiographic Contrast

Film Contrast

Film type

Density

Subject Contrast

Processing Scatter

Wavelength

Screens

Factors Influencing Sensitivity Sensitivity Contrast

Film speed

Screens

Time

Energy

Temperature

Definition

Vibration Geometry

Type

Strength

Processing

Agitation

Radiographic Contrast

Poor contrast Poor contrast High contrast

Radiographic Density The DEGREE OF DARKENING of a processed film is called FILM DENSITY. Film Density is a logarithmic unit: Where I1 is the incident light intensity and I2 is the transmitted light intensity Thus if Film Density = 2, the incident light intensity is 100x greater than the transmitted intensity * Greater contrast is achieved at higher density

Radiographic Density The ratio of transmitted light for densities of 1.0 and 2.0 is a factor of 10, i.e. 10 times more light passes through the radiograph for a density of 1.0 than for a density of 2.0. The minimum density in the area of interest, required by specifications is typically between 1.5 and 2.5. The maximum density stated in a specification will typically be 3.0 or 3.5.

Radiographic Density Lack of Density

Excessive Density

„

Under exposure

„

Over exposure

„

Developer temp too low

„

Excessive development

„

Exhausted developer

„

Developer temp too high

„

Developer too weak

„

Too strong a solution

„

Insufficient development time

Measuring Radiographic Density „

Density is measured by a densitometer

„

A densitometer should be calibrated using a density strip

„

A strip of film containing known densities on the same viewer which is to be used for interpreting the radiograph.

4.0

3.5

3.0

2.5

2.0

1.5

1.0

What is a good radiograph?